1. Field of the Invention
The present invention relates to a vehicle reversing radar, and more particularly to an ultrasonic sensor assembly for the radar.
2. Description of Related Art
A conventional vehicle reversing radar is generally installed at a rear bumper of a vehicle. The vehicle reversing radar has an ultrasonic sensor, in which a ceramic chip in a polarized electric field, due to the anti-piezoelectricity, will make an aluminum housing vibrate and send ultrasonic signals, and will receive the reflected ultrasonic signals from an obstacle within an effective distance. Thus, a driver will know the situation behind the vehicle during reversing without having to stop looking to the front of the vehicle.
A good ultrasonic sensor should send ultrasonic signals in a concentrated area and generates intense reflections from the obstacle to achieve a sensitive detecting effect. With reference to FIG. 5, a conventional ultrasonic sensor's sensitive area, under a test reception sensitivity of −6 dB, has a linear distance along its axis of 250 cm, and a sensitive included angle at 200 cm above 60 degrees. Therefore, the conventional sensor's performance has a low precision.
In some vehicles, a plurality of conventional ultrasonic sensors is installed on the front and rear bumpers. A monitor is provided under an instrument panel of the vehicle for displaying which ultrasonic sensor has detected an obstacle. However, as the conventional ultrasonic sensor has a wide sensitive included angle, they must be respectively installed at ends of the bumpers for preventing the ultrasonic signals from interfering with each other. Nevertheless, the distances between the respective ultrasonic sensors are so big that the detecting precision is still low.
Furthermore, when parking the vehicle, the ultrasonic sensors often detect other parked vehicles beside the vehicle as obstacles, so the driver may be confused by these false alarms.
Therefore, the invention provides an improved ultrasonic sensor to mitigate or obviate the aforementioned problems.